GNU Linux/Ubuntu

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These are my notes for various Ubuntu tasks.

Determining the version of the running kernel

From the Ubuntu kernel wiki page [1]:

The official version of an Ubuntu kernel is found in the /proc/version_signature file. This file contains both the full Ubuntu version of the kernel and the mainline version on which it is based. The first field is always Ubuntu, the second field is the Ubuntu kernel version, and the final field is the upstream version.

From an Ubuntu 14.04 box:

$ uname -a
Linux r2d2 3.13.0-46-generic #77-Ubuntu SMP Mon Mar 2 18:23:39 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/version_signature
Ubuntu 3.13.0-46.77-generic 3.13.11-ckt15

Packages

Package install status cloning

NOTE: For whatever reason, I've not had any reliable results with this approach since moving to Ubuntu 12.04 and newer. I just manually install packages now.

Other descriptions:

  • Ubuntu cloning
  • Ubuntu install cloning
  • etc

Steps

  1. sudo dpkg –-get-selections > packages.txt
  2. Copy packages.txt to the remote machine
  3. sudo dpkg –-set-selections < packages.txt
  4. sudo apt-get dselect-upgrade

Viewing installed packages

  • dpkg --get-selections | grep -v deinstalled
  • dpkg -l | grep -Ev '^rc'


Listing dependencies of a package

[2] [3]

  1. dpkg -I FILE.deb
  2. apt-cache depends package_name
  3. apt-cache showpkg package-name

This latter command shows dependencies of packages in the repos. It's pretty verbose.

Listing reverse dependencies

[4]

  1. aptitude why $package
  2. apt-cache rdepends $package


Cleaning out old kernels

For this example, we want to keep these two kernels and get rid of all the others.


We first get the list of kernels installed. I've intentionally trimmed the list to 10 lines.

dpkg --get-selections | grep linux-image
root@silo:~# dpkg --get-selections | grep linux-image | tail -n 10
linux-image-2.6.32-38-generic-pae               install
linux-image-2.6.32-39-generic                   install
linux-image-2.6.32-39-generic-pae               install
linux-image-2.6.32-40-generic                   install
linux-image-2.6.32-40-generic-pae               install
linux-image-2.6.32-41-generic                   install
linux-image-2.6.32-41-generic-pae               install
linux-image-generic                             install
linux-image-generic-pae                         install
linux-image-server                              install

As you can see in the list, linux-image-2.6.32-41-generic* is the last one in the list and uname -r confirms the currently running kernel:

2.6.32-41-generic-pae

We'll want to leave that one in place, so we'll need to exclude it from the list that we'll be removing. There are a LOT of ways this could be done, but the approach below is the one I use for copying/pasting into remote terminals.

# Set a variable in the shell that contains MOST of the current running kernel. If
# we match exactly we'll exclude any pae or non-pae versions of the kernel
CURRENT_KERNEL=$(uname -r| cut -c 1-15)
 
FILTER_OUT="(deinstall|linux-image-generic|linux-image-server|linux-image-virtual|${CURRENT_KERNEL})"
 
MATCH_ON_REGEX='\<linux-image[0-9.a-zA-z-]+\>'
 
# Print a list of kernels we'll be removing
for kernel in $(dpkg --get-selections | grep -viE "${FILTER_OUT}" | grep -iEo "${MATCH_ON_REGEX}"); do echo $kernel; done
 
# Start the removal process
for kernel in $(dpkg --get-selections | grep -viE "${FILTER_OUT}" | grep -iEo "${MATCH_ON_REGEX}"); do apt-get remove --purge $kernel; done

If you're looking for a script that you can run instead of having to copy/paste the code, this is the same as above with just a few more lines:

#!/bin/bash
 
# Set a variable in the shell that contains MOST of the current running kernel. If
# we match exactly we'll exclude any pae or non-pae versions of the kernel
CURRENT_KERNEL=$(uname -r| cut -c 1-15)
 
FILTER_OUT="(deinstall|linux-image-generic|linux-image-server|linux-image-virtual|${CURRENT_KERNEL})"
 
MATCH_ON_REGEX='\<linux-image[0-9.a-zA-z-]+\>'
 
 
echo -e "\n\nPress Enter to remove these kernels or Ctrl-C to Cancel:\n"
 
# Print a list of kernels we'll be removing
for kernel in $(dpkg --get-selections | grep -viE "${FILTER_OUT}" | grep -iEo "${MATCH_ON_REGEX}"); do echo -e "    * $kernel"; done
 
read TEMP_VAR
 
# Start the removal process
for kernel in $(dpkg --get-selections | grep -viE "${FILTER_OUT}" | grep -iEo "${MATCH_ON_REGEX}"); do apt-get remove --purge -y $kernel; done


Removing packages with 'rc' status [5]

Before I knew better I removed old kernel packages with just apt-get remove X instead of also using --purge to completely remove the package and all associated content. Unfortunately because I forgot to use --purge I cannot use apt-get remove to finish the removal. Thankfully we can use dpkg --purge to finish the job.

dpkg -l |awk '/^rc/ {print $2}' | xargs sudo dpkg --purge

Use with caution!

Thankfully I backed up /etc prior to doing so, but on an Ubuntu 14.04 box I found many instances of packages with the rc status. I removed all of them using the above example and X refused to load. I reverted using the tarball I created just prior to running the command and all was well.

Disabling/Removing whoopsie package [6]

As said better elsewhere:

What's whoopsie? It's the "Ubuntu Error Reporting" daemon, and is installed by default in both desktop/server installations. When something crashes, whoopsie does two things: #1) Collects the crash report generated by Apport and #2 can send them to Ubuntu/Canonical (specifically to https://daisy.ubuntu.com

It can be disabled by setting the report_crashes parameter to false in the /etc/default/whoopsie file. It can be removed via apt-get purge whoopsie,


VMware

Ubuntu as a VMware guest

VMware Tools: Installing the appropriate kernel headers for compilation

sudo apt-get install linux-headers-$(uname -r)


Shared Folders: correct fstab options

Assuming:

  • User Id is 1000
  • /mnt/hgfs folder exists
  • VMware Tools are installed
  • You don't need the mount points available at boot
.host:/ /mnt/hgfs vmhgfs defaults,ttl=5,uid=1000,gid=1000,nobootwait 0 0


Building VMware Tools

First, mount the tools installer iso from VMware Workstation, the vSphere Client or VMware Fusion. Then proceed with these steps. Note the suggestion about running the tools installer manually the first time.

cd /tmp
mount /dev/sr0 /media
tar zxf /media/VMware*.gz
cd vmware-tools-distrib
 
# You probably want to run this manually the first time so your system-specific settings are set
# Note: Not sure where they're stored, but they appear to be saved between tool rebuilds
./vmware-install.pl  --default


Remote Access

Enabling VNC Server

Start at boot

  1. Login as USER [7]
  2. vncpasswd
  3. sudo nano /etc/rc.local
  4. su - user -c "cd /home/user/ && vncserver :1 -geometry 1024x768 -depth 24" 2>/dev/null &

Enable Gnome

nano /home/user/.vnc/xstartup

Include the following:

xrdb $HOME/.Xresources
xsetroot -solid grey
#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &

# Fix to make GNOME work
export XKL_XMODMAP_DISABLE=1
/etc/X11/Xsession


Firewall

Quick UFW rule list

  1. Set the default rule to deny everything
    ufw default deny
  2. Allow in web traffic from "the world" to port 80
    ufw allow 80
  3. Allow ssh from a trusted network
    ufw allow from 192.168.0.0/24 to any port 22
  4. Enable the rules we've just set
    ufw enable
  5. Show the enabled rules
    ufw status


Networking

Disable IPv6

[8]

Modify /etc/sysctl.conf add add this to the bottom:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

Run sudo sysctl -p


References

  1. Ubuntu wiki - How can we determine the version of the running kernel?
  2. http://stackoverflow.com/questions/4627158/howto-list-all-dependencies-of-a-package-on-linux
  3. http://askubuntu.com/questions/80655/how-can-i-check-dependency-list-for-a-deb-package
  4. http://askubuntu.com/questions/128524/how-to-list-package-dependencies-reverse-dependencies
  5. APT Tip: Purge Removed Packages
  6. askubuntu.com - What is the 'whoopsie' process and how can I remove it?
  7. USER is a non-root account that the vncserver will be running as
  8. How to disable IPv6 on Ubuntu?